Optical scanner devices are well-known in the art and may be used to produce machine-readable image data signals that are representative of a scanned object, such as a photograph or a page of printed text. In a typical scanner application, the image data signals produced by an optical scanner may be used by a personal computer to reproduce an image of the scanned object on a suitable display device, such as a CRT or a printer.
A hand-held or portable optical scanner is an optical scanner which is designed to be moved by hand across the object or document being scanned. The hand-held scanner may be connected directly to a separate computer by a data cable. If so, the data signals produced by the hand-held scanner may be transferred to the separate computer "on the fly," i.e., as the image data are collected. Alternatively, the hand-scanner may include an on-board data storage system for storing the image data. The image data may then be downloaded to a separate computer after the scanning operation is complete via any convenient means, such as a cable or an optical infrared data link.
Hand-held or portable optical scanners are well-known in the art and various components thereof are disclosed in U.S. Pat. No. 5,552,597 of McConica for "Hand-Held Scanner having Adjustable Light Path", U.S. Pat. No. 5,586,212 of McConica, et al., for "Optical Wave Guide for Hand-Held Scanner," U.S. Pat. No. 5,381,020 of Kochis, et al., for "Hand-Held Optical Scanner with Onboard Battery Recharging Assembly," and U.S. Pat. No. 5,306,908 of McConica, et al., for "Manually Operated Hand-Held Optical Scanner with Tactile Speed Control Assembly," all of which are hereby incorporated by reference for all that they disclose.
A typical hand-held optical scanner may include illumination and optical systems to accomplish scanning of the object. The illumination system illuminates a portion of the object (commonly referred to as a "scan region"), whereas the optical system collects light reflected by the illuminated scan region and focuses a small area of the illuminated scan region (commonly referred to as a "scan line") onto the surface of a photosensitive detector positioned within the scanner. Image data representative of the entire object then may be obtained by sweeping the scan line across the entire object, usually by moving the hand-held scanner with respect to the object. By way of example, the illumination system may include a plurality of light emitting diodes (LEDs), although other types of light sources, such as fluorescent or incandescent lamps, may also be used.
A typical scanner optical system will include a slit aperture and lens assembly to focus the image of the scan line onto the surface of the detector. Depending on the particular design, the scanner optical system may also include one or more mirrors to "fold" the path of the image light, thus allowing the optical system to be conveniently mounted within a relatively small enclosure. In order to allow a smaller detector array to be used, most optical systems also reduce the size of the image of the scan line that is focused onto the surface of the detector. For example, many optical systems have a lens reduction ratio of about 8:1, which reduces the size of the image of the scan line by a factor of about 8. Such optical systems may be referred to herein in the alternative as "lens reduction" optical systems. In an alternative arrangement, the optical system may include a "contact image sensor" or CIS to focus the image of the illuminated scan line onto the surface of the detector.
The photosensitive detector used to detect the image light focused thereon by the optical system typically comprises a charge-coupled device (CCD), although other devices may be used. A typical CCD may comprise an array of individual cells or "pixels," each of which collects or builds-up an electrical charge in response to exposure to light. Since the quantity of the accumulated electrical charge in any given cell or pixel is related to the intensity and duration of the light exposure, a CCD may be used to detect light and dark spots of an image focused thereon.
The term "image light" as used herein refers to the light that is focused onto the surface of the detector array by the optical system. Depending on the type of scanner and the type of document, the image light may be reflected from the object being scanned or it may be transmitted through the object. The image light may be converted into digital signals in essentially three steps. First, each pixel in the CCD detector converts the light it receives into an electric charge. Second, the charges from the pixels are converted into analog voltages by an analog amplifier. Finally, the analog voltages are digitized by an analog-to-digital (A/D) converter. The digital signals then may be processed and/or stored as desired.
Generally speaking, the portable or hand-held scanners of the type described above may be classified into one of two size groups: Full size and miniature. As its name implies, full size hand scanners are sized so that they may scan a full size document (e.g., letter or legal sized paper) in a single pass. Accordingly, the full size scanner will typically have a scan line length that is approximately commensurate with the shortest dimension of the document to be scanned, e.g., typically about 8.5 to 9 inches or so. While such full size scanners exist and work well, they are not particularly "portable" particularly if they utilize "lens reduction" optical systems, which typically have long optical paths requiring a substantial amount of space. While the overall size of a full size scanner can be reduced by utilizing a CIS optical system, such CIS optical systems generally provide for reduced image quality compared to lens reduction optical systems. Moreover, the color performance of such CIS systems is typically poor, making them unsuitable for use in color scanners.
Miniature scanners are generally considerably smaller than full-size scanners and typically have a scan line length of no more than about 4.5 to 5 inches. As a result, most miniature scanners require multiple passes in order to scan a full size document. While such multiple pass scanning can be performed, it generally requires that the scanner be provided with some type of navigation system to allow the scanner to track its position over the document being scanned. Position data produced by the navigation system allows the image data collected during multiple scanning passes to be later combined or "stitched" together in order to produce image data representative of the entirety of the scanned object. While such scanner navigation systems are known and being used, they are complex and add to the overall cost of the scanner. Also, in order to keep the overall size of such miniature scanners to a minimum, most miniature scanners forego lens reduction optical systems in favor of CIS optical systems. Unfortunately, however, as discussed above, most CIS systems suffer from poor image quality and color performance when compared to lens reduction optical systems.
Consequently, a need exists for a miniature scanner that is capable of scanning full sized documents with a single pass, yet still be small enough to be considered portable. Such a scanner would thereby dispense with the need for an expensive and complex scanner navigation system. Additional advantages could be achieved if such a scanner utilized a high performance optical system, but without significantly impacting the portability of the scanner. Still other advantages could be realized if such a portable scanner were capable of color scanning.